The present invention relates to a process for producing glucose isomerase by culturing strains of Microbacterium or mutations thereof.
Sweet syrups are widely used in the baking, confectionery and beverage industries, for example. These syrups generally consist of sucrose (cane sugar) or dextrose-containing products obtained from starch hydrolysis as the principal sweetening agent. When a syrup is needed that is sweeter than that obtained from sucrose, an invert sugar syrup is employed. This is produced by acid hydrolysis of sucrose to produce a mixture of about 50 percent glucose (dextrose) and about 50 percent fructose (levulose). While glucose is somewhat less sweet than sucrose, fructose is considerably sweeter than sucrose so that the overall sweetness is increased as compared to sucrose.
It is well known that dextrose can be converted under alkaline conditions to fructose. This conversion has great potential value in the production of sweet syrups. However, the alkaline conversion has not been commercially successful because the alkaline reaction produces an undersirably high ash level in the product syrup which is uneconomical to remove. The syrup is not acceptable unless this ash is removed. Alkaline isomerization and its attendent problems are discussed in U.S. Pat. No. 3,383,245.
The prior art then turned to an enzyme conversion of glucose to fructose. It was found that species of Pseudomonas hydrophila, Streptomyces flavovirens, Streptomyces achromogenus, Streptomyces echinatur, Streptomyces albus, Streptomyces olivaceus, Bacillus coagulans, Microbacterium arborescens (formerly classified as Flavobacterium arborescens and Bacillus licheniformis, for example, could be grown in appropriate nutrient media to form enzymes having glucose isomerase properties. This is described, for example, in U.S. Pat. Nos. 2,950,228, 3,616,221, 3,625,828, 3,979,261, 4,061,539 and 4,348,480. The screening of many strains of bacteria for the production of glucose isomerase was reported by suekane, M. et al., Z. Alegemeine Microbiologie 21, 457 (1981). Suekane et al. reported that M. lacticum and Brevibacterium imperiale (reclassified as M. imperiale) did not grow on xylose and did not produce glucose isomerase. M. laevaniformens was formerly classified as Corynebacterium laevaniformans. Suekane et al. tested several species of Corynebacterium and reported that none of these species produced glucose isomerase. Consequently, none of the known prior art suggests the use of strains of the species Microbacterium imperiale, M. lacticum, M. ammoniaphilum or M. laevaniformans to produce a glucose iosmerase.